Under noisy conditions, hearing impaired persons are severely disadvantaged compared to those with normal hearing. As a result of reduced cochlea processing, hearing impaired persons are typically much less able to distinguish between meaningful speech and competing sound sources (i.e., noise). The increased attention necessary for understanding of speech quickly leads to listener fatigue. Unfortunately, conventional hearing aids do little to aid this problem since both speech and noise are boosted by the same amount.
Compression algorithms used in some hearing aids boost low level signals to a greater extent than high level signals. This works well with low noise signals by raising low level speech cues to audibility. At high noise levels, compression performs only modestly since the action of the compressor is unduly influenced by the noise and merely boosts the noise floor. For persons that frequently work in high ambient sound environments, this can lead to unacceptable results.